Often right around that 22 inches in length point is where, depending on the lathe, they have to remove the barrel.
Defensive Edge Rifles has shortened up some of my barrels before they threaded them without unscrewing them from the action and one of them is 20.5 so they could probably do it for you. One of them I had lopped off down to 18in and threaded but it had to be unspun from the action.